Emulsions are mixtures of two or more immiscible liquids, such as oil and water, stabilized by the addition of an emulsifying agent.
Basis of emulsion classification:
Emulsion can be classified into two types on the following two points
- nature of the dispersed phase.
- and continuous phase.
Theories of emulsions
Following theories describe the different types of emulsions:
Oriented wedge theory
This theory explain the formation of water-in-oil (W/O) emulsions.
This theory has following main points :
- The emulsifying agent used in the preparation has both hydrophobic and hydrophilic ends,letting it to interact with both immiscible liquids.
- The emulsifying agent is added to the mixture of water and oil, and it position itself at the interface between the two liquids.
- The emulsifying agent containg two ends
- Hydrohobic end showing attraction towards the oil phase.
- while the hydrophilic end is attracted towards the water phase.
- The emulsifying agent, arrangement at the interface forming a (wedge-like structure) giving stability to emulsion.
- The wedge-like structure decrease the interfacial tension between the two liquids, letting them to fuse and form a stable emulsion.
Draw back of oriented wedge theory:
- Farther types of emulsions, such as oil-in-water (O/W) emulsions, are not described by the oriented-wedge theory.
NOTE:
Overall, the oriented-wedge theory provides a basic understanding of the mechanism behind the formation of W/O emulsions and is widely accepted in the field of emulsion science.
phase inversion theory
This theory describe the formation of oil-in-water (O/W) emulsions.
Main points of this theory is given below:
- An emulsifying agent is used to add in mixture of oil and water.
- Effect of concentration of emulsifying agent:
- At small concentrations of the emulsifying agent, it is favourably adsorbed at the oil-water interface, resulted in formation of water-in-oil (W/O) emulsion.
- As the concentration of the emulsifying agent is increased, it begins to adsorb more at the water-oil interface.
- Inversion point:
At a critical concentration of the emulsifying agent, known as the inversion point.
following things can be happened on inversion point
- The emulsion undergoes a phase inversion
- and becomes an O/W emulsion.
- The inversion point depends on various factors such as
- the nature of the emulsifying agent
- the concentration of the emulsifying agent
- and the properties of the immiscible liquids.
- The phase inversion theory is useful in the design and optimization of emulsion formulations, as it gives information about the factors
- that affect the stability
- and type of emulsion formed.
NOTE:
Overall, the phase inversion theory is an essential idea in emulsion science and provides a framework for understanding the formation of O/W emulsions.
Film Droplet Balance Theory
This theory explains the formation and stability of both
- water-in-oil (W/O)
- and oil-in-water (O/W) emulsions.
This theory have following main points:
- Emulsion droplets are considered as a liquid film that surrounds a core of one of the immiscible liquids.
- The film consists of a layer of emulsifying agent that adsorbs at the interface between the two liquids, forming a monolayer.
- The monolayer decrease the interfacial tension among the two liquids, allowing them to mix and form an emulsion droplet.
- The stability of the emulsion droplet depends on the
- balance of forces acting on It which includes
- the interfacial tension
- the pressure difference across the droplet interface
- and the thickness of the film surrounding the droplet.
- The interfacial tension have a tendency to shrink the droplet, while the pressure difference across the droplet interface have the ability to expand the droplet.
- The thickness of the film surrounding the droplet also affects its stability, its thicknes provide greate stability to it.
- The film droplet balance theory is helpful in understanding the factors:
- that affect the stability of emulsions
- and can be used to optimize the formulation of emulsions.
NOTE:
Overall, the film droplet balance theory provides a valuable framework for understanding the stability of emulsions and is widely used in emulsion science.
Diffusion Controlloed Theory
The diffusion-controlled theory is a theory that gives information about the stability of emulsions based on;
- the rate of diffusion of the emulsifying agent between the two immiscible liquids.
This theory contain following important points:
- Emulsions are stabilized by
- the adsorption of an emulsifying agent at the interface between two immiscible liquids.
- The rate of diffusion of the emulsifying agent molecules between the two liquids governs the stability of the emulsion droplets.
- Effect of rate of diffution:
If the rate is too slow
- the emulsion droplets may coalesce and separate
- leading to the breakdown of the emulsion.
If the rate is too fast
- the emulsifying agent may be rapidly depleted
- leading to the destabilization of the emulsion.
- The stability of the emulsion can be optimized by adjusting
- the emulsifying agent concentration
- droplet size distribution
- and other factors to ensure that the rate of diffusion is optimal.
- The diffusion-controlled theory is useful in
- predicting the stability of emulsions
- and in designing emulsions with specific properties.
NOTE:
Overall, the diffusion-controlled theory provides a valuable framework for understanding the stability of emulsions and is widely used in emulsion science.